The increase in computing power and spatial densities in semiconductor based devices and energy efficiency of the same allow for ever more efficient and small microelectronic sensors, processors and other machines. These have found wide use in mobile and wireless applications and other industrial, military, medical and consumer products.
Even though computing energy efficiency is improving over time, the total amount of energy used by computers of all types is on the rise. Hence, there is a need for even greater energy efficiency. Most efforts to improve the energy efficiency of microelectronic devices has been at the chip and transistor level, including with respect to transistor gate width. However, these methods are limited and other approaches are necessary to increase device density, processing power and to reduce power consumption and heat generation at the same time.
One field that can benefit from the above improvements is switched inductor power conversion devices. Power supplies include power converters that convert one form of electrical energy to another. A regulated power supply is one that controls the output voltage or current to a specific value; the controlled value is held nearly constant despite variations in either load current or the voltage supplied by the power supply's energy source.
In microelectronics fabrication, polymer-based materials are used for photoresists, which are photoimageable (light-sensitive) materials used in photolithography. Photolithography is a process that is used to pattern films or substrates of microelectronic components for device fabrication. Photoresists such as polyimide can also provide electrical insulation in fabricated devices. Such photoresists are thermoset polymers that are deposited, patterned, and cured during fabrication. Once cured, these polymers also provide excellent mechanical and thermal stability and chemical resistance. Curing is a type of heat treatment that is dependent on the temperature, time and ambient environment. For fabrication of CMOS compatible thin-film inductors, photoresist polymers are cured to provide permanent electrical insulation between the inductor coils and the magnetic core layers. In addition, the cured photoresist polymers provide stress-relief due to the presence of large tensile or compressive stresses in adjacent metal and magnetic layers.
Underfill epoxies were developed to increase the reliability of solder bumps and allow for flip chip assembly, a lower cost assembly method for microelectronic components on substrates. These epoxies are polymer-based materials that provide electrical insulation and adhesion between microelectronic components. They mitigate the stresses associated with thermal mismatch between electronic packaging and silicon layers. They also alleviate stresses resulting from electrical, mechanical and thermal cycling typical in microelectronic operation. Underfill epoxies are typically thermoset polymers that are in a viscous state that changes irreversibly into an insoluble polymer network by curing. These epoxies are composites of a polymer resin and hardener that are selected based on the required viscosity, or “ability to flow,” of the underfill between the components. The viscosity of the underfill epoxy is important because the epoxy needs to fill any voids between the microelectronic components to which the epoxy is providing adhesion before the it is cured. The curing process causes reactions to take place between the resin and hardener that results in cross-linking where the precursor materials rigidize into a network of permanently shaped molecules. A cured underfill epoxy provides excellent mechanical and thermal stability.